Since a positive type photosensitive resin which is convertible to a soluble form through photolysis with an active radiation such as ultraviolet ray and the like is, in general, far excellent in respect of resolving power to a negative type photosensitive resin, it is now widely used in the manufacture of integrated circuit, printed circuit board and the like as an etching resist.
Most popular positive type photosensitive resinous compositions comprise an alkali soluble novolak resin added with a quinone diazide compound.
However, such quinone diazide compound is comparatively unstable in heating and must be used in fairly large quantity so as to be effective as a solubilization inhibitor prior to photolysis step.
Furthermore, there are such problems as inferior flexibility of the formed resist film and poor adhesion properties thereof.
Furthermore, since the base material is a novolak resin, there is a drawback of excessive brittleness of the resist film prepared and adhesion between the base plate and the formed resist film is no good.
Quinone diazide will show a strong absorption at preferable wave lengths in an ultraviolet region, and therefore, a resinous composition containing such compound will hardly transmit active radiation in the ultraviolet region, resulting in comparatively poor photolysis especially at the interior.
To solve the abovementioned problems, the inventors have previously proposed a positive type photosensitive resinous composition containing iminosulfonate groups (Japanese Patent Publication (unexamined) No. 163736/89).
As an additional approach for obtaining far improved sensitivity and resolving power, a method has been proposed wherein a secondary decomposition is caused by utilizing an acidic material generated through a photolysis reaction, thereby solubilizing the resist resin (as in Japanese Patent Publication (unexamined) Nos. 45439/84 and ibid 250642/88).
In that method, as an acid source, use is made of an onium salt and thus produced acid is utilized in causing the successive reaction to produce a photo-soluble functional group.
For example, Japanese Patent Publication (unexamined) No. 45439/84 describes a resist composition comprising a polymer having acid-unstable branched groups, e.g. t-butyl ester of carboxylic acid and t-butyl carbonate of phenol, and an onium salt.
Japanese Patent Publication (unexamined) No. 250642/88 describes a radiation sensitive composition comprising a phenol novolak resin, an organic polymer having acid-unstable groups (e.g. polystyrene having t-butyl ester side group or t-butyl ether side group and the like), and an aryl onium salt.
However, in the former technique of using a resin having iminosulfonate groups, sulfonic acid groups are generated by photolysis reaction, which are then neutralized to solubilize the resin. Therefore, in that technique, the iminosulfonate group content should be at least 1.5.times.10.sup.-4 equivalent/g or more, and however, since too much quantity may result in a large quantity of azine and ketone by-products and cause adverse effect on solubility of the resin, its upper limit should be confined to 2.5.times.10.sup.-3 equivalent/g.
Thus, there are naturally limits on solubility of the resin and resolving power of the resist.
On the other hand, in the latter technique of using an onium salt, since the onium salt is hardly soluble in an organic solvent and deficient in compatibility with a resinous material, there is a limit on the resolving power of the resist made of the resinous composition with dispersed onium salt therein. Moreover, there are additional problems such that toxic or undesired metals as stibonium, antimonium and the like are co-present in the system and such resist is very expensive and unsuitable for commercial production.
It is, therefore, an object of the invention to provide a novel positive type photosensitive resinous composition based on a base resin containing iminosulfonate groups which can be decomposed through irradiation by radiations with 200 nm to 400 nm wavelengths and generate strong sulfonic acid groups, which is free from metal onium salt having adverse effects on device characteristics and having toxic properties, and characterized by having far desirable solubility properties and improved resolving power.